The invention relates to a method and corresponding device for burning-off precious metal-containing materials.
The following methods are customary on an industrial scale for the processing of precious metal-containing waste materials with relatively high organic fractions, such as catalyst residues, printed circuit boards and other electronic scrap:                1. Ecolyst® method (Umicore), described in German Patent DE 32 23 501C1/C2. This is a method for precipitation of, mainly, Rh from liquid organic residues through the use of tellurium. An organic mixture remains after separation of the precious metal and must be disposed of (e.g., by combustion). The method requires continuously transportable material.        2. Aquacat® method (Johnson Matthey). This method can be used to process waste materials that contain carbon and organic compounds and precious metals, in particular gold, silver, platinum, and palladium waste from industrial production and the watch and jewelry industry. The organic components are oxidized with oxygen in supercritical water under pressure, with the precious metal remaining behind as an oxidic residue. As before, the material must be continuously transportable. In addition, the method requires a pressurized reactor.        
The aim is for an improved method possessing the following advantageous features:                1) Batch-wise or continuous processing with the option of continuous operation;        2) Efficient control of the thermal economy; and        3) High yield of the valuable substances.        
The direct combustion (burning-off) of the organic fractions of precious metal-containing residues is already being utilized in various methods. Methods for the combustion of precious metal-containing sludges and multi-element waste with subsequent leaching of the ash are described, for example, in German Patent DE 31 34 733 C2 and International Patent Application Publication WO 99/37823. However, if the residues to be treated contain organic fractions that combust very easily and with great energy, there may be very intensive flame formation.
Siemens KWU developed a method for the treatment of private household waste, in which pyrolysis and high temperature combustion with utilization of the pyrolysis gases were combined (Ullmann's 6th ed., CD-ROM-Release 2003, “Waste” Ref 320: K. J. Thomé-Kozmiensky: Thermische Abfallbehandlung, EF-Verlag für Energie- and Umwelttechnik, Berlin 1994). However, the crucial factor therein is the production of energy during combustion (waste power plant).
Another possible method is the gasification of the organic fractions of metal-containing waste. German published patent application DE 33 29 042 A1 relates to a method for the recycling of non-ferrous heavy metals and precious metals from plastic-containing materials, in particular from coking products, in which the carbon is gasified under isothermal conditions with a separately generated gasification agent, such as H2O/CO2/O2, whereby the temperature is regulated by the partial pressures. However, this method also is associated with major equipment needs and the presence of significant fractions amenable to gasification at all times, since the gas ultimately serves to produce energy.
German Utility Model DE 94 20 410 U1 relates to a facility for a thermal recycling method for metallic objects that are mixed with or contaminated by organic substances, e.g., oil barrels, but also, on a smaller scale, precious metal-containing sweepings from jewelry workshops or small operations of the jewelry industry. Carbonization in the presence of a pyrolysis phase and an oxidation phase in a carbonization chamber is recommended in this context, whereby the oxidation proceeds with the introduction of a waste gas with a combustible oxygen content. According to German published patent application DE 35 18 725 A1, a similar facility serves for thermal varnish removal—in this case, including the combustion of the carbonization gases.
The two methods are not suitable for liquids with organic fractions that combust with great energy.